Versatile Hall magnetometer with variable sensitivity assembly for characterization of the magnetic properties of nanoparticles

Abstract

 A Hall magnetometer with variable sensitivity is constructed to measure the magnetic properties of magnetic nanoparticles manufactured by different methods. This novel magnetometer can also be used to measure bulk materials and samples in liquids. The magnetometer is constructed with two commercial Hall-effect sensors in an acrylic structure, which serves as the support for a micrometer and the circuit board with the sensors. For operation, the magnetometer it acquires a complete magnetization curve in a few minutes. If has a magnetic moment sensitivity of 1.3 × 10 -9 Am 2 to sensitivity of 493 mV/mT, the sensitivity can be adjustable in the range of 10 to 493 mV/mT. Its performance is tested with magnetic nanoparticles. As an application example, we estimate the mean diameter of the nanoparticles using the magnetic curves. The results are compared with those obtained by other techniques, such as transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic light scattering (DLS). The magnetization results are also compared with those obtained by independent commercial magnetometers, which reveals errors of approximately ±0.31 Am 2 /kg (i.e., 0.6%) in the saturation region.

A Review of Characterization Techniques for Ferromagnetic Nanoparticles and the Magnetic Sensing Perspective

“…The magnetometer is a widely used device for many scopes, including biomedical purposes, geophysical studies, non-destructive testing, and catalytic materials characterization [58]. To serve the last scope, namely magnetic nanoparticle sensing, in the international literature exist several magnetometers, like the vibrating sample magnetometers (VSM), the optically pumped magnetometers (OPM), the magneto-optical Kerr effect magnetometers, the giant magnetoresistive sensors (GMR) [37,59], the alternating gradient magnetometers, the Faraday rotation magnetometers, the Hall effect magnetometers, the superconducting quantum interference devices (SQUIDs), the fluxgate magnetometers, etc., each with different sensitivity and cost [60,61]. In this paragraph, the most important types of magnetometers are presented and compared with their advantages and disadvantages.…”

Scanning Magnetic Microscope Using A Hall-Effect Sensor for Images of Remanent Magnetization Fields

“…This calibration is very important because it is through this calibration that we have the accuracy of the equipment. In order to verify the assembly capability, we used only circuit boards and compared the measurements with magnetic maps obtained with commercial equipment, such as the lock-in amplifier (SR560, SRS Inc.) using the same 99% purity nickel sphere, which was analyzed after being magnetized by a 0.5 T field, and magnetic microparticles of Fe3O4 obtained by the coprecipitation method [10][11][12]. Thus, we made scanning magnetic maps of the x-and y-axes (Figure 4c -4f).…”

Scanning Magnetic Microscope Using a Gradiometric Configuration for Characterization of Rock Samples

“…The calibration process of the magnetic microscope consists of acquiring the distance on the z-axis between the sensitivity region of the Hall-effect sensors and the surface of the sample using only circuit boards and measuring the sample remanent fields with a 99% purity nickel sphere magnetized at 0.5 T to determine the distance [13][14][15]17,18]. The nickel sphere was placed in a sample holder made of acrylic material with a cylindrical cavity (see Figure 2a).…”

“…Thus, we made scanning magnetic maps of the x-and y-axes ( Figure 2b,e,g). Unlike the calibration process, the maps of Figure 2d,e were obtained after the nickel In order to verify the assembly capability, we used only circuit boards and compared the measurements with magnetic maps obtained with commercial equipment (as shown in the ESI), such as the Lock-In amplifier (SR560, SRS Inc.), using the same 99% purity nickel sphere, which was analyzed after being magnetized by a 0.5 T field, and magnetic microparticles of Fe 3 O 4 obtained by the coprecipitation method [14,18]. Thus, we made scanning magnetic maps of the x-and y-axes ( Figure 2b,e,g).…”

“…The standard deviation of the measurements was approximately 0.04 × 10 −10 Am 2 (about 0.38%) for the remanent magnetization. A low-cost device capable of filtering and amplifying the signals collected by the Hall-effect sensors, with the same quality as similar equipment offered in the market, was also developed, making it accessible and operational in academic environments [16][17][18]. We tested the device's performance with magnetic microparticles, containing a core of iron oxide and geological samples.…”